1,721,004 research outputs found
Comprensione dei meccanismi che governano effetti potenzialmente negativi dei nanomateriali nei confronti dei sistemi biologici
No full textMentre le nanotecnologie si sviluppano e producono decine di prodotti contenenti materiali nanostrutturati che sono già disponibili sul mercato, lo studio delle proprietà esclusive di questa categoria di materiali rimane lacunosa e ancora meno studiate sono le proprietà che danno genesi ad effetti di tossicità verso l’uomo, gli animali o l’ambiente.
Proprio mentre aumenta la domanda sociale di consapevolezza riguardo al ciclo di vita dei prodotti, il settore dei nanomateriali fornisce informazioni insufficienti e lo sviluppo di queste tecnologie rischia di essere rallentato dalla diffidenza del mercato. Per garantire il progresso è necessario bilanciare l’avanzamento tecnologico e la conoscenza tossicologica dei materiali sviluppati.
Al giorno d’oggi, quando si esegue un progetto di sviluppo di un nanomateriale inedito, si ha come principale attenzione la funzionalità che questo dovrà ottemperare. È necessario che questi studi siano affiancati da valutazioni di tipo ecologico e tossicologico dei materiali sviluppati: il miglior materiale in termini di efficienza deve rispettare anche le cosiddette esigenze EHS, ossia rispettare ambiente, salute e sicurezza (con particolare riguardo ai problemi di produzione).
Infine, per essere pienamente sostenibili, i nuovi prodotti devono essere anche economicamente sostenibili, ovvero non rinunciare ai vantaggi delle nanotecnologie con strategie di riduzione del rischio che rendano i prodotti meno competitivi perché gravosi economicamente o legati all’impiego di risorse limitate.
Per avvicinarsi a queste necessità, la strategia proposta in questo lavoro si fonda sullo sviluppo di produzioni progettate per essere sicure: concentrando le attenzioni sulla produzione del materiale nanostrutturato in modo che sia esso stesso in grado di limitare la propria pericolosità, si consente al nanomateriale di inserirsi in qualsiasi processo produttivo senza preoccupazioni circa il rischio.
Per i materiali tradizionali questa pressione allo studio delle pericolosità intrinseche non è avvertito poiché sono materiali conosciuti all’uomo da tempo, molti nanomateriali invece vengono specificatamente ingegnerizzati per intensificare le proprietà desiderate, questo significa che sono totalmente nuovi all’uomo e non esistono osservazioni a medio-lungo termine del loro comportamento.
Se si dovesse studiare il comportamento di un nuovo materiale si potrebbe svolgere uno studio sperimentale approfondito del suo comportamento, la particolarità dei nanomateriali però è che a seguito di piccole fluttuazioni di una variabile (ad esempio il diametro di una nanopolvere) consegue una grande variazione del comportamento. In altre parole è necessario considerare per la stessa sostanza infiniti diversi materiali per ogni diversa combinazione delle possibili variabili. In laboratorio non è possibile effettuare uno studio sistematico e completo, è necessario sfruttare nuove tecniche di simulazione che tengano in considerazione le variabili in gioco e controllino il comportamento simulato dei materiali confrontandolo con poche prove sperimentali mirate e molto ben caratterizzate.
I modelli matematici estrapolati da queste simulazioni devono poi essere integrati con ulteriori aggiornamenti del comportamento dei nanomateriali indotti dalle condizioni ambientali. Lo stesso materiale potrebbe risultare innocuo o pericoloso in funzione di variabili ambientali.
Queste simulazioni hanno quindi molteplici finalità: completare la conoscenza dei nanomateriali, indicare quali tecniche di ingegnerizzazione rispondono meglio alla riduzione dei rischi, prevedere la pericolosità di un prodotto nanotecnologico e fornire alla collettività uno strumento con cui decidere se consentire o bandire l’impiego delle sostanze
Pyroshock Testing: A Theoretical and Experimental Investigation for the Qualification of Aerospace Equipment
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Progress in pyroshock simulation for qualification tests: A systematic literature review
Full text linkpacecraft and their onboard equipment are subjected to significant dynamic loads, particularly when the activation of pyrotechnic devices induces intense high-frequency shocks, known as pyroshocks, which propagate throughout the entire structure and can cause critical damages. Qualification tests are needed to ensure aerospace equipment can withstand impulsive loads and therefore test rigs and simulation models are designed to replicate real-world pyroshocks while pursuing repeatability, accuracy, and safety.
This paper systematically categorizes and analyzes existing research papers on pyroshock simulation techniques, examining both experimental and numerical approaches. Scientific databases were queried but only a selection of the most relevant papers is presented and labeled, according the publication year, the purpose, the physical domain, the numerical method, the kind of fixture, and the excitation method. Additionally, a shorter review on contact mechanics is included to offer complementary insights, considering its relevance to pyroshock simulations
Optimization of irregular-shaped resonant plates for pyroshock testing in the aerospace industry
No full textThe simulation of pyroshock tests through resonant plates is a standard procedure to verify the resistance of space equipment to high-frequency shocks generated by pyrotechnic devices. These shocks lead to significant risks, potentially compromising missions. Space qualification criteria - typically expressed in Shock Response Spectrum (SRS) terms - vary based on launch vehicle characteristics and follow the guidelines provided in international standards such as the NASA-STD-7003A. This study employs a frequency domain-based numerical model and a heuristic optimization algorithm to optimize resonant plate designs, considering irregular quadrilateral shapes. Integrating a CAD modeler, finite element solver, and genetic algorithm optimizer improves SRS prediction accuracy, reduces calibration times, and minimizes trial-and-error repetitions. While adopted decisions may influence specific outcomes, this work outlines a general methodology applicable across diverse requirements and constraints
Syntactic categories for Nori motives
No full textWe give a new construction, based on categorical logic, of Nori’s Q-linear abelian
category of mixed motives associated to a cohomology or homology functor. This new construction makes sense
for infinite-dimensional vector spaces as well, so that it associates a Q-linear abelian
category of mixed motives to any (co)homology functor
Condition monitoring of an industrial book-cutting machine using a novel mixture of vibration and physics-based features
No full textThis study presents an enhanced approach to machinery diagnostics and prognostics, using artificial intelligence and machine learning to improve vibration monitoring systems for industrial equipment maintenance. Targeting a complex automatic book-cutting machine, the proposed diagnostic system integrates a mixture of diverse feature types, combining accelerometric data with physics-based features to provide a more comprehensive and accurate monitoring solution. A dataset, developed through a full factorial design of experiments, covers a range of operational states, while data processing generates an optimal feature set for maintenance decision-making. This hybrid approach, exploiting the novel combination of features, offers superior identification of machine states of health compared to traditional vibration monitoring, generating benefits such as reduced downtime and costs, as well as enhanced product quality. In the specific application analyzed, the proposed method improved classification accuracy by approximately 7% compared to traditional vibration monitoring techniques. By integrating these advancements, achieved through sensor fusion and multi-channel data, into a Supervisory Control And Data Acquisition (SCADA) system, this research aligns with the goals of Industry 4.0, supporting digital and cyber-physical manufacturing systems with an intelligent, data-driven condition-based maintenance strategy suitable for modern automated environments
Numerical Modeling of a Pyroshock Test Plate for Qualification of Space Equipment
Full text linkOver their life, space equipment needs to withstand strong high-frequency shocks, which could cause mission and safety critical damages. In order to verify the compliance with safety standards, pyroshock tests are employed. Based on launch vehicle characteristics, the requirements for the qualification of space equipment are usually established following the NASA-STD-7003A international standards in terms of a Shock Response Spectrum (SRS) representing the damage potential of the shock. Laboratory tests should then match the actual stress conditions reached during a real launch. Historically, this was obtained by means of explosive charges (hence the name “pyroshock”). Nevertheless, to foster repeatability and safety in laboratories, hammers or bullets are commonly used in nowadays shock testing machines.
In this work, a resonant fixture test bench is considered. In this very common layout, a resonant metallic plate is interposed between the impact location and the test component so as to better simulate the shocks. The response of the resonant plate - which determines the required shock response spectrum - is currently empirically tuned by adding masses, damping, stiffness, or by varying the nature of the impact. This study aimed at developing a numerical model able to completely simulate a pyroshock test. Such a model can be used both for designing and for tuning the test bench so as to easily match different SRS requirements for different components under test. This leads to great economical advantages as can cut the calibration times leading to more efficient and effective testing
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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